It is proposed to produce several monoclonal antibodies against the EGF receptor purified by affinity chromatography from the solubilized plasma membranes of A-431 human epidermoid carcinoma cells, based on preliminary studies in which clones are obtained (and are at hand) which secrete antibodies against the receptor. The antibodies detected by a solid phase immunoassay procedure, will be screened for their ability to inhibit the binding of 125I-EGF and/or the EGF-stimulated phosphokinase activity of the receptor, and to immunoprecipitate the solubilized receptor. The antibodies will be used to visualize immunocytochemically EGF receptors on the surface and interior of A-431 cells maintained in serum-free media with and without EGF. The goal is to establish whether EGF receptors occur within the cell or cell organelles in unstimulated cells. In addition, we will test whether binding of antibodies to the receptor is sufficient to produce a physiologic response, i.e. stimulation of cell replication or replacing EGF in maintaining Hela cells in serum-free medium, thus mimicking the action of EGF.